Optical assembly/housing for securing optical fiber components, devices and fibers to the same or to mounting fixtures

ABSTRACT

A method of bonding glass-based optical elements comprising the steps of positioning a first glass-based optical element relative to a second glass-based optical element, applying a glass-based bonding compound about the first and second optical elements, and applying sufficient localized heat to the glass-based bonding compound to cause the glass-based bonding compound to soften and fuse with the optical elements.

FIELD OF INVENTION

This invention relates generally to optical fibers, fiber opticcomponents and devices, and more particularly to securing opticalfibers, components or devices to mounting fixtures or other opticalcomponents and devices.

BACKGROUND OF THE INVENTION

Over the last 15 years, a number of fiber optic components and devicessuch as: couplers, attenuators, wavelength divisionmultiplexers/demultiplexers, connectors, filters, switches,fiber-pigtailed semiconductor lasers, isolators, etc., have beendeveloped for use in fiber optic communication systems, sensors andinstrumentation. In nearly all of these applications employing fiberoptic components or devices, design-specific mounting fixtures areutilized to precisely align, position or secure optical fibers orelements within such optical fiber components or devices. In most ofthese applications, it is common for such mounting fixtures to be formedof a fused silica material because its low coefficient of thermalexpansion closely matches that of the optical fibers and other opticalcomponents or devices. In this respect, maintaining the stability andrelative position of optical fibers, components or devices, through thecorrect choice of materials, is particularly critical in that even minorrelative movements between such elements may result in large variationsor degradation in optical characteristics, such as coupling ratios andinsertion losses.

Optical fibers, components and devices are typically secured to a baseplate or substrate with an epoxy material. The two most common types ofepoxy adhesives used in these applications cure upon exposure to eitherUV light or heat. The epoxy adhesives are widely used because they areinexpensive, easy to use and in many instances, readily cured. Rapidin-situ cure schedules are also well suited for volume manufacturing.

While epoxies offer a convenient means for attaching optical fibers,components or devices to substrates or to other optical fibers,components or devices, the physical properties of cured epoxies oftenmake such materials less than ideally suited for use in fiber opticsystems. In one respect, epoxies typically possess very differentcoefficients of thermal expansion relative to the optical fibers,mounting substrates, optical components and devices they are used tosecure. This difference may affect the stability and relative positionof the respective components or devices when exposed to temperaturechanges. In another respect, epoxies have a tendency to absorb moisture.Such tendency is detrimental in that moisture significantly reduces anepoxy's ability to firmly secure the optical fiber, optical componentsor devices to other optical fibers, components or devices or to asubstrate. In addition, the cured epoxy swells as it absorbs watervapor, and this swelling may strain the relative attachment betweenoptical fibers, or optical components, or optical devices, or thesupporting substrates. In general, moisture induced swelling andsubsequent degradation of the epoxy adhesive may cause misalignment oreven detachment of the optical fibers, components or devices relative toa supporting substrate or other optical elements. Additionally, epoxiesexhibit physical degradation from prolonged exposure to environmentalconditions, such as thermal, oxidative and photo degradation which maycause a further breakdown of the epoxy structure over such periods ofexposure.

As fiber optics continue to penetrate the telecommunications market,product lifetimes of 20 years or more will be mandatory. In order toachieve this degree of performance, new packaging techniques andmaterials, other than epoxies, will be required for reliably attachingoptical fibers, components or devices to supporting substrates and toeach other. Ceramic based cements or adhesives may be used in someapplications as an alternative to epoxies since these materials areparticularly impervious to moisture. One major disadvantage associatedwith their use, however, is that they require long cure schedules, oftenat elevated temperatures, which for example, substantially hinder theirusefulness in high volume production.

A large variety of glass powders, commonly known as glass frits are usedfor making joints or seals. These materials are used for making strong,insulating and often hermetic connections between different materialssuch as glass, ceramics or metals. Due to the inorganic nature of thesematerials, these materials are particularly impervious to moisture. Theyconsist of various metal oxides such as lead, boron and zinc. However,most of these frits exhibit large coefficients of thermal expansion,typically 10 to 100 times larger than that of silica. Furthermore, theuse of these frits requires subjecting the assembled article to longannealing schedules in order to prevent the formation of fractures andalso temperatures of between 400° C. to 1000° C. are typically required.However, since the acrylate buffer coating on optical fibers is damagedat 150° C., the buffer precludes the use of furnace based techniquestraditionally used to soften and anneal such glass materials. Thisdisparity in the coefficients of thermal expansion, in the event a glassfrit with a typical coefficient of thermal expansion is used as anattachment material, may result in the occurrence of a stress at theinterface between the fused glass frit and the optical fiber, component,device or support substrate. Such stress may be relieved through theformation and propagation of a crack within the fused glass frit oroptical fiber, device or component (cohesive failure) or by theseparation of the fused glass frit at the glass frit/optical fiber,device or component interface (adhesive failure). Such cohesive oradhesive failure is undesirable.

The present invention overcomes these and other problems and provides animproved method of using a glass composition for securing opticalfibers, components and devices to mounting fixtures or to other opticalfibers, components or devices, which method of securing creates a bondbetween such components that is less susceptible to physical degradationfrom exposure to adverse environmental conditions and that reduces thelikelihood of deterioration of the performance of such components as aresult of such exposure than bonding procedures known heretofore.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide means for attachingoptical fibers, components or devices to substrates or to other opticalfibers, components or devices. Optical fibers, devices, components orsubstrates will be individually or collectively referred to as a "fiberoptic element" or as "fiber optic elements," respectively.

It is another object of the present invention to provide means forattaching optical fibers, a plurality of optical fibers held together orattached by supporting means, components or devices to substrates orother optical fibers, components or devices which provide superiorstability and long term performance under prolonged exposure toenvironmentally adverse conditions.

Another object of the present invention is to provide a means forattaching optical fibers, components or devices to substrates or otheroptical fibers, components or devices wherein epoxy is not a primarymeans of securing the respective fibers, components, devices andsubstrates.

Another object of the present invention is to provide a bondingcomposition for attaching optical fibers, components or devices tosupport substrates or other optical fibers, components or devices,wherein the bonding composition includes a metal-oxide based bondingcomponent, an organic binder and a vehicle.

Another object of the present invention is to provide means forattaching optical fibers, components or devices to substrates or otheroptical fibers; components or devices wherein the fused bondingcomponent of the bonding composition has thermal expansion propertiessimilar to that of the optical fibers, components, devices orsubstrates.

A still further object of the present invention is to provide a bondingtechnique as described above which provides optical fibers, components,devices or fiber support substrates with increased service life.

A still further object of the present invention is to provide a bondingtechnique as described above which minimizes the changes in the opticalperformance of components or devices such as changes in the "insertionloss" or "coupling ratios" of the fiber optic components or devices.

A still further object of the present invention is to provide a bondingtechnique as described above which reduces the likelihood of degradationof the performance of the optical fibers, components or devices.

A still further object of the present invention is to provide not only adesirable bond between fiber optic elements, but to provide moistureimpervious bonds that result in hermetic seals, thereby protecting thebonded elements from moisture, vapors, including water vapor, and gasesthat would adversely affect the performance of the fiber optic elements.

In accordance with the present invention, there is provided a method ofbonding glass-based optical fibers, components or devices to each otheror to glass or ceramic based substrates comprising the steps of:positioning a first glass-based optical element relative to a secondglass-based optical element; applying a bonding composition contiguousto at least one of the first and the second optical elements, thebonding composition comprised of a mixture of a metal-oxide-basedbonding component, a binder component and a vehicle component, andapplying sufficient localized energy to the bonding composition to causethe metal-oxide based bonding composition to soften sufficiently to wetthe surfaces of the optical elements and bond thereto.

In accordance with another aspect of the present invention, there isprovided a method of bonding at least one first glass-based element toat least one second glass-based element comprising the steps of:positioning at least one first glass-based optical element relative toat least one second glass-based optical element; positioning a glass incontact with the first and second optical elements, the glass having asurface energy less than the surface energy of the first optical elementor the second optical element; and causing the glass to be heated untilthe glass has softened and formed ionic bonds with the first opticalelement and the second optical element.

In accordance with another aspect of the present invention, there isprovided a method of securing at least one fiber optic coupler to aglass support substrate comprising the steps of: positioning at leastone fiber-optic coupler on a glass support substrate; applying a bondingcompound to the coupler, or couplers, and substrate, the bondingcompound comprised of a mixture of glass particulate and an organicbinder in a vehicle, the particulate having a coefficient of thermalexpansion approximately equal to that of the coupler, or couplers, andthe substrate, and having a surface energy which is less than thesurface energy of the coupler, or couplers, or the substrate; andheating the substrate with laser energy until the glass particulatesoftens and wets the surfaces of the coupler, or couplers, and thesubstrate and bond thereto.

In accordance with another aspect of the present invention, there isprovided a method of bonding glass-based optical elements comprising thesteps of: positioning at least one optical fiber relative to aglass-based optical element, applying a glass-based compound about theoptical fiber, or fibers, and the optical element, applying sufficientlocalized heat to the glass-based compound to cause the glass-basedcompound to soften, wet the surfaces of the optical fiber, or fibers,and the optical element and bond thereto.

In accordance with another aspect of the present invention, there isprovided a method of bonding glass-based optical elements comprising thesteps of: positioning at least one optical element relative to anoptical waveguide, applying a glass-based compound about the opticalelement, or elements, and said waveguide, and applying sufficientlocalized heat to the glass-based compound to cause the glass-basedcompound to soften, wet the surfaces of the optical element, orelements, and the waveguide, and bond thereto.

In accordance with another aspect of the present invention, there isprovided, a fiber optic assembly formed of a first glass-based elementand a second glass-based element joined together by the steps of:positioning the first glass-based optical element relative to the secondglass-based optical element, applying a glass-based compound about thefirst and the second optical elements, and applying sufficient localizedheat to the glass-based compound to cause the glass-based compound tosoften, wet the surfaces of the optical elements and bond thereto.

This invention further provides a method of bonding glass-based opticalelements comprising the steps of positioning at least one firstglass-based optical element relative to at least one second glass-basedoptical element; applying a glass-based compound about said first andsaid second optical elements; applying sufficient localized heat to saidglass-based compound to cause said glass-based compound to soften, wetthe surfaces of said optical elements and bond thereto.

DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, embodiments of which will be described in detail in thespecification and illustrated in the accompanying drawings wherein:

FIG. 1 is a schematic representation of a portion of a fused fiber opticcoupler and a support substrate;

FIG. 2 is a schematic representation of an apparatus for use inattaching optical fibers, components or devices to substrates or toother optical fibers, components or devices, such as the coupler andsubstrate shown in FIG. 1;

FIG. 3A is an enlarged, top plan view showing a portion of a fusedcoupler bonded to a support substrate in accordance with the presentinvention;

FIG. 3B is a sectional view taken along lines 3B--3B of FIG. 3A;

FIG. 4 is an enlarged sectional view showing glass fibers of a couplersupported on a glass substrate, and graphically illustrating a bondingcompound comprised of glass particulate in a binder matrix for securingsame;

FIG. 5 is a sectional view of the fibers and substrate shown in FIG. 4,graphically depicting the glass particulate after it has been bonded tothe glass fibers and glass substrate;

FIG. 6 is an enlarged sectional view of an optical fiber disposed withina ceramic ferrule;

FIG. 7 is an enlarged perspective view of a planar waveguide componentwith optical fibers attached thereto; and

FIGS. 8A, 8B and 8C are views of an optical element housing.

DESCRIPTION OF PREFERRED EMBODIMENT

Broadly stated, the present invention relates to packaging, positioningand securing optical fibers, components or devices to a supportsubstrate or to other optical fibers, components or devices by means ofa bonding composition. As generally understood in the art, the term"components" generally refers to passive fiber optic apparatus, and theterm "devices" generally refers to active fiber optic apparatus.Hereinafter, components and devices shall refer to the generallyaccepted definitions as given above. The bonding composition isgenerally comprised of a metal-oxide based component, preferably inparticulate form, a binder component and a vehicle component. Theoptical fibers, components or devices are positioned relative to eachother, and the bonding compound is applied contiguously to thecomponents. Intensive energy is applied locally to the bondingcomposition to heat same to a temperature at which the binder componentpreferably burns away completely and the residual metal-oxide basedcomponent drops sufficiently in viscosity so that it flows over and wetsthe surfaces of the fibers, components or devices wherein such elementsare bound together upon cooling. It is believed that some of the vehiclecomponent may evaporate prior to heating. Any vehicle remaining prior toheating evaporates or is burned off during application of the intensiveenergy. It is further believed that some or all of the binder componentis burned away during application of the intensive energy. Importantly,the energy applied is maintained within a predetermined range which issufficient to cause the metal-oxide based component to soften and flow.

Referring now to the drawings where the purpose is for illustrating apreferred embodiment of the invention only and not for purposes oflimiting the same, FIG. 1 is a schematic view of a portion of a fusedoptical coupler 10 which is to be mounted to a support substrate 20 inaccordance with the present invention. The present invention shall bedescribed with particular reference to the fiber optic coupler 10 andsupport substrate 20 arrangement shown in FIG. 1, however, it shall beappreciated from a further reading of the specification that the presentinvention has broader applications in the field of fiber optics. Morespecifically, the present invention finds advantageous application in"packaging," securing or bonding a variety of optical fibers, componentsor devices. In this respect, the present invention may be utilized inpackaging, positioning or connecting, optical fibers, a plurality ofoptical fibers held together by supporting means, couplers, connectors,attenuators, wavelength division multiplexers/demultiplexers,connectors, filters, switches, fiber pigtailed semiconductor lasers andisolators, and other glass-based elements. As set forth above, thepresent invention provides a means for securing a first optical fiber,component or device to a second optical fiber, component, device orsubstrate. In the embodiment shown in FIG. 1, the first optical elementis comprised of a fiber optic coupler 10 and the second element is asupport substrate 20 to which the coupler is to be attached. In FIG. 1,only half of the fiber coupler 10 is shown, it being understood that theother half of coupler 10 is similarly configured and is to be mounted tosubstrate 20 in a similar manner. Coupler 10 is comprised of fusedside-by-side optical fibers 12, 14. An acrylate buffer 16 on fibers 12,14 has been previously removed to expose glass fibers 12, 14, which arejoined at a coupling region 18 by conventionally known techniques. Toprovide support to coupler 10, it is typically mounted to a substrate20. Substrate 20 is typically formed of a silica-based glass materialhaving a coefficient of thermal expansion closely matching that ofsilica glass optical fibers 12, 14.

In the embodiment shown, substrate 20 is a cylindrical rod having alongitudinally extending groove 22 formed therein. Groove 22 isgenerally defined by a pair of planar, sloping side surfaces 24, 26 anda planar bottom surface 28.

It will of course be appreciated, that a substrate 20 may have othershapes or configurations without deviating from the present invention.For example, substrate 20 may be other than a cylindrical rod. In thisrespect, substrate 20 may be an elongated rod having, for example, acircular, elliptical, rectangular or prismatic cross section. Further,such a rod-shaped substrate 20 may or may not have a longitudinal groovetherethrough. Basically, substrate 20 can assume any configuration whichsupports or contains the optical fiber, element or component to bemounted thereto.

In accordance with the present invention, coupler 10 is generallypositioned on substrate 20, as shown in FIGS. 3A and 3B. Individualfibers 12, 14 that are fused to form the fiber optic coupler may bemounted to substrate 20 by a small amount of UV curing epoxy, designated30 in the drawings. Epoxy 30 is preferably confined to the regions offiber 12, 14 where acrylate buffer coating 16 has not been removed. Atthis point, the primary purpose of epoxy 30 is to hold coupler fibers12, 14 in place on support substrate 20 while coupler 10 is subsequentlysecured to the substrate 20 by the method to be described hereinafter.With respect to holding coupler fibers 12, 14 in place, it will ofcourse be appreciated that other means such as mechanical fasteners, orother materials such as hot melt adhesives or other adhesives such asurethanes, acrylics, cyanoacrylates, water based adhesives or any otherpolymeric based adhesives could be used to temporarily hold coupler 10in place on support substrate 20.

With coupler 10 positioned on substrate 20, a bonding composition,designated 40 in the drawings, is applied to coupler 10 and substrate 20in the areas where coupler 10 is to be attached or secured to substrate20. According to a preferred embodiment of the present invention,bonding composition 40 is specifically formulated to be both chemicallyand physically compatible as an adhesive with glass-based elements(i.e., to be compatible as an adhesive with the glass forming thesubstrate and the fibers of the coupler). Bonding composition isprimarily comprised of a metal-oxide based solid amorphous material.

As used herein, the term "solid" refers to material ranging from athree-dimensional macroscopic member to a fine powder. Preferably, themetal-oxide based material is in powder form and when in this form ismixed with a binder component and a vehicle component. The mixture ofthe bonding component (i.e., the glass-based material), the bindercomponent and the vehicle component, may range in consistency from athick, cementitious paste to a sprayable slurry. In this respect,depending upon the nature of the optical elements to be bound and themanner in which the bonding composition is to be applied, theconsistency of bonding composition 40 may be varied by varying theamounts and relative percentages of the respective components.

More specifically, the bonding component of bonding composition 40 ispreferably a powdered mixture of silica and metal oxide based glasses.The binder component, typically nitrocellulose, is included in thecomposition solely to provide the powder with some "green strength"before it is heated. In other words, the binder component is provided toimpart some dimensional stability to the glass-based particulate toenable the particulate to be positioned relative to coupler 10 andsubstrate 20. Importantly, the bonding component, (i.e., the glasspowder) is formed of a glass or a ceramic, that when fused, has athermal coefficient of expansion equal to, or approximately equal to,the thermal coefficient expansion of the glass material forming thefiber optic elements to be joined or secured. In the present embodimentshown, the thermal coefficient of expansion of the glass powder, and thefused glass resulting from the thermal fusion of the glass powder, wouldgenerally be equal to the thermal coefficient of expansion of coupler 10and substrate 20.

Importantly, in addition to being a metal-oxide material and having acoefficient of thermal expansion equal to or approximately equal to thecoefficient of thermal expansion of the optic elements to be secured,the glass powder forming the bonding component also preferably has asurface energy less than the surface energy of the optical fibers,components, substrate or devices to be secured. In this respect, asshall be described in greater detail below, the glass-based component ofbonding composition 40 is provided as the adhesive or bonding materialwhich will adhere the fiber optic elements together. While the glasspowder and glass forming the fiber optic elements are similar materials,they are not identical and therefore "adhesive" forces (as distinguishedfrom "cohesive" forces) will hold the respective materials together atthe adhesive/adherend interface. Inasmuch as "wetting" is critical togood adhesions(Wetting is the sine qua non of adhesion), it is importantthat the surface energy of the glass powder be less than the surfaceenergy of the optical elements to be bonded, as this will allow for goodsurface "wetting" and good adhesion. Accordingly, because it is theglass powder which forms the bonding or adhesive material, and it is thesurface energy of the glass powder which is of importance, the surfaceenergy of the glass powder should be less than the surface energy of thematerials to be adhered.

Bonding composition 40 is preferably applied only a few millimetersalong the length of exposed coupler fibers 12, 14. According to thepresent invention, intensive energy is applied locally to bondingcomposition 40 by means of a laser to heat the same. A carbon dioxide(CO₂) laser is preferably used in that such a laser has a specificoptical wavelength, approximately 10.6×10⁻⁶ meters. In addition to theglass powder of the glass bonding material, the silica based opticalfibers, devices, components and substrate are all capable of absorbingelectromagnetic radiation at the wavelength of a CO₂ laser as quotedabove.

With no intent to be bound, it is believed that the glass powder andfiber optic elements heat up in accordance with the followingexplanation. The glass powder and fiber optic elements have a largeabsorptivity for electromagnetic radiation at the above-quotedwavelength of light. In effect, the complex portion of the dielectricfunction is large for the glass powder and fiber optic elements at thewavelength of the carbon dioxide laser as quoted above. The electronicnature of the glass powder and the fiber optic elements is such that theincident electromagnetic radiation at the above-quoted wavelength isabsorbed and subsequently transformed into heat as the glass atoms andtheir associated electrons move more rapidly in response to the drivingforce of the incident electromagnetic radiation. The enhanced motion ofthe atoms and electrons comprising the glass powder or fiber opticelements is a result of the coupling between the incidentelectromagnetic radiation and the electrical charges and chargedistributions present in the glass powder or fiber optic elements. Inthis respect, the bonding compound or preferably one of fiber opticelements is exposed to a laser beam with the above referenced wavelengthat a sufficient power level such that the bonding composition or fiberoptic element is heated rapidly. This affects the bonding composition orfiber optic element in several ways. As previously mentioned, as thelaser beam illuminates the bonding composition and the substrate, theglass molecules, atoms and electrons therein absorb the laser energy andincrease their average velocity. Heat from the glass powder or thesubstrate which results from the absorption of the electromagneticradiation by the glass powder or the substrate is absorbed by theorganic binder which burns away. As previously mentioned, the organicbinder is pyrolyzed, but the heating is so short-lived that the bindermay not completely burn away. Continued exposure of the glass powder orthe fiber optic element or substrate 20 to the laser beam causes theremaining glass powder to soften sufficiently to wet the surfaces of thefiber optic elements and supporting substrate and to fuse the fiberoptic elements to the silica-based supporting substrate. In the eventthat any one of the fiber optic elements is illuminated with the carbondioxide laser, heat is thermally conducted to the glass bondingcomposition by the fiber optic elements. The illumination of any one ofthe fiber optic elements should continue until sufficient thermal energyis transferred to the glass bonding composition to cause the glassbonding composition to soften sufficiently to wet the surfaces of thefiber optic elements and to cause the fiber optic elements to bondtogether. Importantly, in this respect, the heat which softens the glassbonding composition and causes it to wet and bond to the opticalcomponents may be applied directly or indirectly, depending upon thenature of the type of components to be joined.

With respect to the embodiment shown, it is a preferred method of thepresent invention that the laser beam illuminates glass substrate 20directly. It is a most preferred method of the present invention thatthe portion surface of glass supporting substrate 20 located directlybelow planar bottom surface 28 of groove 22 (i.e., the bottom ofsubstrate 20) be illuminated with the electromagnetic radiation of thecarbon dioxide (CO₂) laser. In all of the above mentioned preferredmethods, thermal energy would be thermally conducted to glass bondingcomposition 40. Illumination should continue until sufficient thermalenergy has been conducted to glass bonding composition 40 to soften theglass powder sufficiently to wet the surfaces of the fiber opticelements (i.e., fibers 12, 14 and substrate 20) and cause the elementsto bond to one another as the glass powder fuses.

Importantly, strong ionic "cohesive" bonds are formed within the fusedbonding glass and strong "adhesive" ionic bonds are formed between thefused bonding glass and the glass material forming the fiber opticcoupler or, fiber optic elements including the supporting substrate. Inother words, as the binder material essentially burns away, the glasspowder essentially fuses together and bonds with the silica-basedelements (i.e., glass substrate 20 and silica-based fiber optic coupler10 or generally, the optical fibers, devices or components) formingionic bonds therewith, which in the embodiment shown secures couplerfibers 12, 14 of coupler 10 to substrate 20 when cooled. The organicbinder is essentially burned away, leaving essentially the glass powder,and perhaps some residual binder material as it is surmised that not allof the binder may burn away, to fuse together and to optical fibers 12,14 and substrate 20 to adhere the same.

With respect to the energy to be applied to bonding composition 40,generally, it is necessary to provide sufficient energy to heat theglass powder component to a softened state sufficient to wet opticalfibers 12, 14, couplers, components, devices and substrate and to fusethe glass powder, but not so much energy as to thermally shock ordestroy the optical elements. In one respect, the energy to be appliedis related to the composition and mass of the bonding component. In thisrespect, the enthalpy H (i.e., the energy under constant pressure)required to soften the bonding component (i.e., the glass powder) of thebonding composition is based upon the following equation:

    H=mC.sub.p T (the "Enthalpy Equation");

where "H" is the enthalpy, "m" is the mass in kilograms of material (theglass powder), "C_(p) " is the specific heat under constant pressure inJoules/Kg°C. of the material, and "T" is the temperature change of thematerial between ambient (i.e., room) temperature and the desiredelevated temperature at which the glass powder softens, wets the fiberoptic elements and fuses (i.e., the desired temperature wherein theglass powder will fuse together and bond to the glass-based fiber opticelements). Accordingly, based upon the amount of bonding compositionutilized, the approximate amount of energy required to cause themetal-oxide based glass powder bonding composition thereof to soften,wet, fuse and bond with the fiber optic elements may be calculated. Itwill of course be appreciated that a certain amount of energy will berequired to heat and burn away some if not all of the binder component.Accordingly, the laser energy required to soften, wet, fuse and bond thebonding composition to the fiber optic elements is roughly dependentupon the amount (i.e., the mass) of the metal-oxide based component(i.e., the glass powder) in bonding composition 40. More energy mayactually be required than predicted by the Enthalpy Equation previouslycited.

Referring now to FIG. 2, a work station 50 including a CO₂ laser 52,some associated beam optics and a motorized work platform 54 forcarrying out the process set forth above, is shown. The fiber opticelements to be joined (i.e., coupler 10 and substrate 20) are positionedon moving platform 54, and laser 52 is reflected onto bondingcomposition 40 by a silicon (Si) reflecting mirror 56.

Referring now to assembly of the coupler and substrate shown in FIG. 1,the following is an example of the procedure outlined above for bondingthe coupler to a glass substrate.

As indicated above, the bonding composition utilized to secure the fusedcoupler to the substrate is comprised of a bonding component (i.e.,glass powder), a binder component, and a vehicle component. Tests wereconducted with a bonding component formed from powdered glass, whereinthe glass had the following composition by weight:

    ______________________________________                                        GLASS COMPOSITION                                                             COMPONENTS         % weight                                                   ______________________________________                                        LEAD OXIDES        <60%                                                       SILICON OXIDES     <30%                                                       ALUMINUM OXIDES    <15%                                                       BORON OXIDES       <10%                                                       ZINC OXIDES        <10%                                                       LITHIUM OXIDES     <10%                                                       ______________________________________                                    

The glass is basically ground into a powder and the binder component ismixed into the glass component of the bonding composition. The bindercomponent is comprised of nitrocellulose. In a preferred embodiment ofthe present invention, the powder is applied in a slurry form afterbeing dispersed in a solvent based vehicle. The vehicle component isformed of amyl acetate (N) mixed with 2-methyl butyl acetate. Thevehicle has a boiling point range of between 83° C. and 146° C. Thevehicle is volatile and evaporates soon after the application of theslurry. The bonding composition used is thus comprised of powdered glassof the type described above, an organic binder as described above and avehicle component as described above. This bonding compound is utilizedto secure a fused fiber coupler to a silica glass support substrate.

As indicated above, coupler 10 is initially positioned on substrate 20by means of an epoxy 30 applied at the ends of the acrylate coating 16.A small amount, from about three to about five cubic millimeters, ofbonding composition 40 is applied to coupler 10 and substrate 20, a fewmillimeters beyond epoxy 30. Substrate 20 and coupler 10 are then placedon moving platform 54 and the carbon dioxide (CO₂) laser beam is appliedto substrate 20 until sufficient thermal energy is thermally conductedto the glass bonding composition 40 such that the glass componentsoftens sufficiently to wet the surfaces of fibers 12, 14 and substrate20 and bond same together as the glass component fuses.

The carbon dioxide laser used has a beam diameter of approximately 3.5mm, a beam power of approximately 3.5W and a beam scanning speedrelative to the optical components of approximately 3 mm/min. The laseris applied to substrate 20 for approximately thirty to sixty seconds. Asindicated above, the electromagnetic radiation indirectly heats theglass powder to a fusion and bonding temperature of approximately380°-400° C. FIG. 2 shows work station 50 having a motorized workplatform 54 for moving the workpiece relative to a stationary laser 52.It will of course be appreciated that heat may also be applied to astationary workpiece by means of a moving heat source.

FIGS. 4 and 5 generally illustrate the foregoing process. In FIG. 4,bonding composition 40 is shown in contact with fibers 12, 14 andsurfaces 24, 26, 28 of substrate 20. In FIG. 4, bonding composition 40is illustrated as comprised of glass particulate (i.e., powder) 42dispersed in binder 44. As will be appreciated, glass particulate 42 isshown in exaggerated form for purposes of illustration. As indicatedabove, binder 44 provides "green strength" or dimensional stability toglass particulate 42 to enable same to be applied about fibers 12, 14and substrate 20. FIG. 5 generally illustrates bonding composition 40after the thermal energy has been applied. In this respect, binder 44has generally been burned away, and glass particulate 42 has bondedtogether and to fibers 12, 14 and surfaces 24, 26, 28 to form a bondtherewith.

It is believed that the bonds formed according to the present inventionbetween the fiber optic elements and the bonding composition may beionic in nature. It is further surmised that London dispersion forcesmay play a part in the bonding between the fused glass bonding materialand the surfaces of the fiber optic elements.

The molecules of the glass powder bond together, and being of likematerial, form cohesive bonds. The molecules of the glass powder incontact with the glass material forming the fiber optic elements, i.e.,fiber 12, 14, (which include supporting substrate 20), being ofdifferent materials, form adhesive bonds with the glass molecules offibers 12, 14. With respect to the later adhesive bonds, the lowersurface energy of the glass powder ensures good "wetting" of the higherenergy surfaces of the fiber optic elements, thereby facilitating goodadhesive bonds therebetween. The resulting glass-to-glass bonds (bothcohesive and adhesive) formed by the bonding composition are very strongand impervious to moisture.

Because the resulting bonding component (i.e., the glass powder) has acoefficient of thermal expansion that closely matches that of the fiberoptic elements (i.e., in the embodiment shown optic fibers 12, 14 andsubstrate 20), misalignment of the components and/or cracking of thebonding material does not occur during thermal expansion or contraction.This matching of the coefficient of thermal expansion between the fusedglass bonding component and the fiber optic elements results in aprevention of stress build-up at the interface of the fused glassbonding material and fiber optic elements.

After fibers 12, 14 have been fused to substrate 20 by the glass bondingcomponent of glass bonding composition 40, it has been discovered thatmotion of the individual optical fibers 12, 14 may result in stressconcentrations within fibers 12, 14 at points where fibers 12, 14 areadhered (i.e., bonded) to the other elements. To alleviate thissituation, in some instances it may be desirable to apply a strainrelief material that would adhere fibers 12, 14 to support substrate 20a short distance from the point where fibers 12, 14 are fused tosubstrate 20. If the strain relief material were flexible, this wouldalleviate the stress build-up in fibers 12, 14 at the point where fibers12, 14 are fused to substrate 20 by the glass bonding component.Parenthetically, this point of fusion is non-forgiving to motion offibers 12, 14 as the glass bonding material has very little flexibility.Any motion of fibers 12, 14 would stress fibers 12, 14 at the pointwhere fibers 12, 14 are fused to substrate 20 due to the inflexibilityof the fused glass bonding component. The flexibility of a strain reliefmaterial should be greater than the flexibility of the fused glassbonding material and hence, more forgiving than the fused glass bondingmaterial. Attachment of fibers 12, 14 by the flexible strain reliefmaterial to supporting substrate 20 would tend to dampen the motion offibers 12, 14 at the point of fusion of the fibers to substrate 20. Thiswould decrease the internal stress build-up within fibers 12, 14 at thepoint of bonding of fibers 12, 14 to substrate 20 which could arise as aresult of flexing.

In this respect, as indicated above, a UV epoxy 30 was originally usedto locate and maintain fiber optic coupler 10 in position on substrate20 during the bonding procedure. The same epoxy 30 may be maintained inits position to act as a strain relief material to minimize the internalstresses within fibers 12, 14 at the point of bonding between fibers 12,14 and substrate 20. It will of course be appreciated that otherarrangements or materials may be utilized to limit the relative motionof the components in the glass-to-glass bonding area. For instance,other flexible strain relief materials and means including mechanicalmeans may be used to attach fibers 12, 14 to supporting substrate 20 ashort distance from the glass-to-glass bonding area. In particular, anymaterial that has a greater flexibility than the fused glass bondingmaterial and that would adhere to fibers 12, 14 and substrate 20, may beemployed as a strain relief material. Further, a hot melt adhesive, aurethane adhesive, a cyanoacrylate adhesive, rubber cement, a waterbased adhesive or any other polymeric based adhesive that would adheregenerally to the fiber optic elements and specifically to optical fibers12, 14 and supporting substrate 20, may be utilized instead of the epoxy30 to confine fibers 12, 14.

According to the present invention, the respective cohesive and adhesiveglass bonds developed within the glass bonding material and between theglass bonding material and the fiber optic elements have been found tobe less susceptible to adverse environmental conditions, and to haveless affect over time, on the operation of the components.

In this respect, the chemical bonds between the fibers and the fusedglass bonding material and between the supporting substrate and thefused glass bonding material did not appear to weaken as a result ofexposure to moisture. Furthermore, by using materials with similarcoefficients of thermal expansion, bonded components and devices areoptically and mechanically very stable under dynamic temperatureconditions.

Not only does the use of the glass bonding composition disclosed in thisinvention result in beneficial attachment means, the disclosed bondingcomposition may be used so as to result in a bond that protects andhermetically seals the fiber optic elements from the adverse effects ofmoisture, vapors, such as water vapor, and detrimental gases.

Further, this new technique for packaging fiber couplers is simple,consistent and may be readily adapted for use in a productionenvironment. It does not significantly add to the time it takes tomanufacture a coupler and does not require the use of any specializedhardware other than the glass bonding material and a method of producingsufficient localized heat to soften the glass bonding material to thepoint at which it wets the fiber optic elements.

While the present invention has been described with respect to securinga coupler to a glass substrate, it will be appreciated that theprocedure described above may be applied to a variety of other opticalfibers, components or devices for securing, locating or positioning samerelative to a glass substrate or other fiber optic components, devicesor fibers. For example, the present invention also finds advantageousapplication in securing an optical fiber 60 to a connector ferrule 62,as shown in FIG. 6.

Heretofore, optical fibers have typically been secured to connectorferrules by means of an epoxy material. The optical fiber is positionedwithin a bore extending axially through the ferrule, and epoxy materialis used to secure the fiber to the ferrule. The end of the fiber and theend surface of the ferrule are then polished to provide an opticalsurface for mating with other connectors. A problem with the use of anepoxy material is that it abrades more rapidly than glass or ceramicmaterial, of which the ferrules are typically formed. This can causesurface imperfections in the optical surface. Further in this respect, aconnector formed with epoxy is subject to the same environmentaldeterioration as discussed above with respect to couplers. In thisrespect, thermal expansion may cause the optical fiber to piston in andout of the ferrule upon thermal cycling. Furthermore, prolonged exposureto humidity may cause the epoxy to deteriorate, thereby weakening theattachment of the fiber to the ferrule.

The present invention provides a means for securing optical fibers toceramic ferrules or even glass ferrules. In this respect, fiber 60 maybe bonded to ferrule 62 utilizing glass-based bonding compound 40.Bonding composition 40 is disposed between the outer surface of fiber 60and the inner surface of bore 64 through ferrule 62. It is advisable toapply a small amount of bonding composition 40 to the tip of ferrule 62and about fiber 60 in order to adequately support the fiber duringsubsequent polishing operations. By directing the optical energy of thelaser onto ferrule 62, bonding composition 40 fuses to both ferrule 62and optical fiber 60. Attaching fiber 60 to ferrule 62 in this mannerprovides a connector less susceptible to degradation as a result ofenvironmental conditions, for the reasons previously mentioned. Further,by utilizing glass-based bonding composition 40, which ionically bondsto the fiber 60 and ferrule 62, the end surfaces of fiber 60 and ferrule62 may be polished and provide a smooth continuous mating surface.

Referring now to FIG. 7, a further application of the present inventionis shown. In FIG. 7 a planar waveguide component 80 is shown havingoptical fibers 82 attached thereto. The ends of optical fibers 82 can beattached to planar waveguide component 80, in optical alignment with theoptical waveguides 84 therethrough, by means of bonding composition 40as outlined above. In this respect, the ends of fibers 82 may be placedin optical contact and alignment with the optical waveguides 84 ofwaveguide component 80, and bonding composition 40 utilized to securesame together. Attaching optical fibers 82 to planar waveguide component80 in this manner provides for a connection that is less susceptible todegradation as a result of environmental conditions, for the reasonspreviously mentioned.

A means for simultaneously joining a plurality or an array of fibers toa planar waveguide component is also contemplated by the presentinvention. For example, a plurality or an array of optical fibers may befirst attached to a supporting member. The ends of each of theindividual optical fibers 82 may then be placed in optical registry withand adhered to the waveguides 84 by the bonding composition and thebonding methods disclosed herein. In another instance, the opticalfibers may be first attached to a supporting member; the ends of each ofthe optical fibers 82 may then be placed in optical registry with thewaveguides 84; and the supporting member may then by attached andadhered to the planar waveguide component by the bonding composition andthe bonding methods disclosed herein. It is contemplated that thesupporting member be made of a material such as glass, preferably glasswith a coefficient of thermal expansion comparable to the coefficient ofthermal expansion of the optical fibers supported thereby, and morepreferably, glass that not only has a coefficient of thermal expansioncomparable to the coefficient of thermal expansion of the optical fiberssupported thereby, but that has a surface energy larger than the glassbonding compound applied thereto.

Referring now to FIGS. 8A, 8B and 8C, a housing 100 for enclosing anoptical element, such as a coupler, is shown. Housing 100 is comprisedof a lower housing section 102 and an upper housing section 104. Lowerhousing section 102 is generally channel-shaped, having a flat bottomwall 106 and upward extending side walls 108. Spaced apart ribs 112project from bottom wall 106 and extend between side walls 108. Upperhousing section 104 is generally a flat planar member dimensioned tomate with lower housing section 102. Spaced apart ribs 114 project fromthe lower surface of upper housing section 104 and extend generally fromside to side. Ribs 114 on upper housing section 104 are disposed to bein registry with ribs 112 on lower housing section 102. Ribs 112 and 114are dimensioned such that a space 116, best seen in FIG. 8C, is definedtherebetween when lower housing section 102 and upper housing section104 are mated together. In this respect, ribs 112, 114 are dimensionedsuch that space 116 is approximately equal to the diameter of a bareoptical fiber 120, which may be positioned therebetween, as shown inFIGS. 8B and 8C. Side walls 108 of lower housing section 102 arepreferably dimensioned such that the spacing between upper housingsection 104 and bottom wall 106 of lower housing section 102 is suchthat the acrylate buffer portion 122 of the optical fiber 120 isconfined therebetween as best seen in FIG. 8B.

According to one aspect of the present invention, upper housing section104 may be secured to lower housing section 102 by applying bondingcomposition 40 along the upper edges of side walls 108, heating sameuntil bonding composition 40 has softened sufficiently to wet therespective mating surfaces of housing sections 102, 104 and bond sametogether. Preferably, bonding composition 40 is also applied in space116 around the bare optical fibers 120. In this respect, by forming aglass bond between ribs 112, 114 and glass fibers 120, together withforming a bond between housing sections 102, 104, the coupler ishermetically sealed within housing 100, thereby preventing exposure ofthe coupler to humidity or other potentially adverse gases. An epoxy(not shown) may also be applied to the distal ends of housing 100 aroundacrylate buffer 122 of optical fibers 120 to secure same to housing 100and to further provide a second barrier layer to environmentally sealthe coupler.

Fiber optic elements may be hermetically sealed to each other by anappropriate use of the glass bonding composition. That is, the glassbonding composition may be placed at points or regions along the fiberoptic elements at which hermetic seals are desired. The glass bondingmaterial is then heated and fused according to the methods disclosedherein. As the fused glass is impervious to water vapor, the fused glassforms, in and of itself, an hermetic seal.

In accordance with another aspect of the present invention, housingsections 102, 104 may be formed of the metal-oxide based silica glass,described above, and ribs 112, 114 may be modified to abut each otherand to include semi-cylindrical recesses specifically formed to supportand confine the bare glass fibers therein. Then, by applying localizedheat along the abutting edges of housing sections 102, 104, and alongthe outer surface of housing sections 102, 104 and in the vicinity ofribs 112, 114, it is possible to bond housing 100 directly to the bareglass optical fibers and seal same. In this respect, the glass forminghousing sections 102, 104 will softened until the engaging surfacesthereof bond together and bond to the glass optical fiber.

As thus shown, the present invention may be used to attach fibersdirectly to other glass elements such as graded-index lenses, mirrors,filters, glass windows or the like. Moreover, the present procedure isnot limited to optical fiber technology, but may be used to securealmost any type of glass element to a glass base substrate. For example,prisms, mirrors, filters, lenses, etc. may be bonded to each other or toother glass-based components according to the present invention. In thisrespect, the present invention may be used to attach optical fiberstogether either end-to-end or side-by-side, and may also be used toaffix glass elements together. Further, while the present invention hasbeen described with respect to a CO₂ laser, alternative heat sourcessuch as lasers in general, a gas burning flame, a small flame from aminiature oxy-acetylene torch, a small electric heater, an electric arc,an infrared heater or ion bombardment may be used to provide the heat tomelt and fuse the metal-oxide based component of the bonding material solong as such heat source has sufficient energy and intensity to softenthe glass bonding material to the point where the glass bonding materialwets the fiber optic elements and is sufficiently localized to avoiddamage to the fiber optic elements.

The foregoing and other modifications will occur to others upon areading and understanding of the specification.

It is intended that all such modifications, alterations and applicationsbe included insofar as they come within the scope of the patent asclaimed or the equivalents thereof.

Having thus described the invention, the following is claimed:
 1. Anassembly comprised of a first element having a glass-based portion, asecond element having a glass-based portion and a glass-based compoundcomprised primarily of metal oxides bonded to said glass-based portionsof said first and second elements, said assembly formed by the stepsof:positioning said glass-based portion of said first glass-basedelement relative to said glass-based portion of said second element;applying a glass-based compound comprised primarily of metal oxidesabout said glass-based portions of said first and said second elements;and applying sufficient heat to said glass-based compound to cause saidglass-based compound to soften, wet the surfaces of said glass-basedportions of said elements and bond thereto.
 2. An assembly as defined inclaim 1 wherein said glass-based compound has a coefficient of thermalexpansion approximately equal to the coefficients of thermal expansionof said first or said second elements.
 3. An assembly as defined inclaim 1 wherein said glass-based compound includes lithium oxides andzinc oxides.
 4. An assembly as defined in claim 3 wherein saidglass-based compound includes glass particulate.
 5. An assembly asdefined in claim 1 or 4 wherein said glass-based compound is primarilyformed of metal oxides having the following approximate composition byweight:

    ______________________________________                                        lead oxides      <60%                                                         silicon oxides   <30%                                                         aluminum oxides  <15%                                                         boron oxides     <10%                                                         zinc oxides      <10%                                                         lithium oxides    <10%.                                                       ______________________________________                                    


6. An assembly as defined in claim 1 wherein said glass-based compoundis comprised primarily of lead oxides, aluminum oxides and siliconoxides.
 7. An assembly as defined in claim 6 wherein said glass-basedcompound is a solid.
 8. An assembly as defined in claim 6 wherein saidglass-based compound has a cementitious, paste-like consistency.
 9. Anassembly as defined in claim 6 wherein said glass-based compound is asprayable fluid.
 10. A housing for encasing at least one glass-basedelement, said housing comprised of at least one housing section formedof a glass-based compound having a coefficient of thermal expansionapproximately equal to said element and having a surface energy which isless than the surface energy of said element, wherein said glass-basedcompound is primarily formed of metal oxides having the followingapproximate composition by weight:

    ______________________________________                                        lead oxides      <60%                                                         silicon oxides   <30%                                                         aluminum oxides  <15%                                                         boron oxides     <10%                                                         zinc oxides      <10%                                                         lithium oxides    <10%.                                                       ______________________________________                                    


11. A housing defined in claim 10 wherein said housing is comprised of aplurality of housing sections having mating surfaces.
 12. A housing asdefined in claim 10, wherein said housing encases and hermetically sealssaid at least one glass-based element.
 13. An optical assembly comprisedof an optical element having a glass-based portion and a glass-basedsupport member formed of a glass material having a coefficient ofthermal expansion which is closely matched to said optical elementchemically bonded to said glass-based portion, said assembly formed bythe steps of:exposing the glass portion of said glass-based opticalelement; positioning the exposed portion of the glass-based opticalelement adjacent to said glass-based support member; directing a laserbeam to said glass-based support structure to cause said structure tosoften in the area of said glass-based portion, to wet the surface ofsaid portion and to bond thereto.
 14. An optical assembly as defined inclaim 13, wherein said glass-based support member is formed primarily oflead oxides.
 15. An optical assembly comprised of:at least one opticalfiber having a glass-based portion; at least one element having aglass-based portion; and a glass-based compound bonded to saidglass-based portion of said optical fiber and to said glass-basedportion of said element, said compound comprised primarily of glassmaterial and having a coefficient of thermal expansion approximatelyequal to the coefficient of thermal expansion of said glass-basedportions of said optical fiber and said element and a surface energyless than the surface energies of said glass-based portions of saidoptical fiber and said element.
 16. An assembly as defined in claim 15,wherein said glass-based compound is formed primarily of lead oxides.17. An assembly as defined in claim 16, wherein said glass-basedcompound includes lithium oxides and zinc oxides.
 18. An assembly asdefined in claim 15, wherein said element is a support element having abore therein receiving said optical fiber.
 19. An assembly as defined inclaim 18, wherein said support element is formed of a ceramic.
 20. Anassembly as defined in claim 15, wherein said optical assembly includesa fiber optic coupler and said element is a support substrate.
 21. Anassembly as defined in claim 15, wherein said element is a housingencasing said coupler.
 22. An assembly as defined in claim 15, whereinsaid glass-based compound hermetically seals said optical fiber to saidelement.
 23. An assembly as defined in claim 15, wherein said element isa waveguide component.
 24. An assembly as defined in claim 15, whereinsaid glass-based compound is primarily formed of metal oxides having thefollowing approximate composition by weight:

    ______________________________________                                        lead oxides      <60%                                                         silicon oxides   <30%                                                         aluminum oxides  <15%                                                         boron oxides     <10%                                                         zinc oxides      <10%                                                         lithium oxides    <10%.                                                       ______________________________________                                    


25. An assembly comprised of:an element having a glass-based portion;and a glass-based element chemically bonded to the glass-based portionof said element, said glass-based element having a coefficient ofthermal expansion approximately equal to the coefficient of thermalexpansion of said glass-based portion of said element and having asurface energy less than the surface energy of said glass-based portionof said element.
 26. An assembly as defined in claim 25, wherein saidglass-based element is a support member formed primarily of lead oxides.27. An assembly as defined in claim 25, wherein said glass-based elementis primarily formed of metal oxides having the following approximatecomposition by weight:

    ______________________________________                                        lead oxides      <60%                                                         silicon oxides   <30%                                                         aluminum oxides  <15%                                                         boron oxides     <10%                                                         zinc oxides      <10%                                                         lithium oxides    <10%.                                                       ______________________________________                                    